As a fan-coupling device of this kind, the interior of a sealing housing constructed by a case and a cover is partitioned into an oil reservoir chamber and a torque transmission chamber for internally mounting a drive disk by a partition plate having a supply adjusting hole of oil. A dam is formed in one portion of the inner circumferential wall face of the sealing housing side opposed to the outer circumferential wall portion of the drive disk for collecting and reservoiring the oil at the rotating time. A circulating flow passage is formed between oil reservoir chambers by the torque transmission chamber so as to be connected to the dam. The fan-coupling device has a valve member for opening the supply adjusting hole of the above partition plate when the temperature of the external circumference exceeds a set value. When the temperature is equal to or lower than the set value or less, the valve member closes the supply adjusting hole of the above partition plate. In a system for controlling the torque transmission from the drive side to the sealing housing side of the driven side by increasing and decreasing an effective contact area of the oil in a torque transmission clearance portion arranged on an opposite wall face near the exterior of the drive disk and the above sealing housing, a pair of electromagnets are arranged on the front face side or the rear face side of the above sealing housing. A valve member is arranged so as to be opposed to one of the electromagnets and has a magnetic property for opening and closing the supply adjusting hole. Further, a sub-valve member is arranged so as to be opposed to the other electromagnet and has a magnetic property for opening and closing the above circulating flow passage (see Japanese Patent No.2911623).
However, the above conventional external control type fan-coupling device has a structure in which the electromagnet and an armature for operating the valve member are separated by the case of a non-magnetic material. Therefore, no magnetic force of the electromagnet can be efficiently transmitted to the armature. Further, excessive electromagnetic force is required to attract the armature, and the size and weight of the electromagnet are increased. Accordingly, problems exist in that no fan-coupling device can be made compact and light in weight and a large amount of electric power consumption is required. Further, when the armature is located in the position separated from a rotating shaft within the oil reservoir chamber, there is a disadvantage in that the operation of the armature, i.e., the operating property of the opening and closing of the valve member becomes worse by receiving the resistance of the oil since the armature always exists within the oil during the rotation of the fan.
Therefore, the present inventors previously proposed an external control type fan-coupling device (JP-A-2003-239741). In this external control type fan-coupling device, a magnetic material of a ring shape is arranged between the above electromagnet and the valve member. The external control type fan-coupling device is constructed so as to assemble the magnetic material into the sealing housing such that a magnetic flux of the electromagnet is transmitted to the valve member through the magnetic material. Thus, the fan-coupling device is made compact and light in weight and electric power is saved and fan rotation controllability is improved.
On the other hand, a viscous fluid joint for transmitting output driving torque to a radiator cooling fan by driving torque from the engine of the vehicle, and its control method are disclosed in JP-A-9-119455. This viscous fluid joint has a system for changing the oil supplying amount by opening and closing the valve by the deformation of a bimetal reacting on the temperature of a passing wind of the radiator, and changing the fan rotation. This system will be explained in more detail. An object of this system is to prevent fan noises and slip heat in a low idle state at the stopping time of the vehicle. In this system, the rotating speed of the vehicle engine is detected and its actually measured value is compared with a limit value set in advance. When the rotating speed of the engine is smaller than the limit value, the rotating speed of the radiator cooling fan is detected and the fan rotating speed is compared with a fan speed limit value determined in advance. In contrast to this, when the fan rotating speed is greater than the limit value, a process for correcting an input signal to move the valve member to the closing position is set.